The synthesis of silicoaluminophosphate molecular sieves with different structures was disclosed in U.S. Pat. No. 4,440,871 in 1984, and these molecular sieves were SAPO-5, SAPO-11, SAPO-16, SAPO-17, SAPO-20, SAPO-31, SAPO-34, SAPO-35, SAPO-37, SAPO-40, SAPO-41, SAPO-42 and SAPO-44. Synthesis of these SAPO molecular sieves is characterized in that a silicon source, an aluminum source, a phosphorus source, and various template agents are employed. The structural units of these SAPO molecular sieves are composed of PO2+, AlO2−, and SiO2 tetrahedrons. Among these kinds of molecular sieves, some microporous molecular sieves, such as SAPO-34, have been successfully applied to the MTG process, MTO process and so on, and show excellent catalytic performance. Since then, some silicoaluminophosphate molecular sieves with new structures have been synthesized subsequently. The emersion of SAPO-8, SAPO-36, SAPO-46, SAPO-18, SAPO-39, SAPO-43, SAPO-47, and SAPO-56 enriched the types of silicoaluminophosphate molecular sieve.
Molecular sieve having a RHO framework structure is formed by connecting a cage by double eight-membered rings, belonging to cubic crystal system. The main channel is composed of double eight-membered rings with a pore-opening size of 0.36 nm×0.36 nm. In 1973, Robson, H. E. et al. firstly reported that a silicon-aluminum zeolite with RHO framework structure was synthesized using Na+ and Cs+ as structure directing agents (Adv. Chem. Ser., 121, 106-115). In 1987, Rouse, R. C. et al. reported the discovery of a natural ores having RHO framework structure (N. Jb. Miner. Mh., 1987, 433-440). Henceforth, BePO (Stud. Surf. Sci. Catal., 1989, 49, 411-420), AlGeO (Microporous Mesoporous Mat., 1999, 28, 139-154), BeAsO (1991, Nature, 349, 508-510), and GaSiO (J. Phys. Chem., 1995, 99, 9924-9932) molecular sieves with RHO framework structure were successively synthesized using Na+ and Cs+ as the structure directing agents. In 1998, Feng, P. Y. et al. reported that CoAPO-RHO, MgAPO-RHO, and MnAPO-RHO molecular sieves were synthesized using N,N′-diisopropyl-1,3-propanediamine as template agent (Microporous Mesoporous Mat., 23, 315-322). Hee-Young Jeon, et al. used several microporous molecular sieves with eight-membered ring channels for the synthesis of methylamine and dimethylamine (Appl. Catal. A, 2006, 305, 70-78), and found that RHO zeolite had more than 90% catalytic selectivity for methylamine and dimethylamine, which was the best catalytic selectivity comparing with several other molecular sieves. Mohamed H, Farid Nouar, Tao W, et al. respectively reported that RHO-MOFs were used as hydrogen storage materials and achieved a series of research progress. (J. AM. CHEM. SOC. 2008, 130, 12639-12641; J. AM. CHEM. SOC. 2009, 131, 2864-2870; J. AM. CHEM. SOC. 2009, 131, 6111-6113). Recently, our laboratory has reported the synthesis of SAPO molecular sieves with RHO framework structure (named DNL-6).